1. Field of the Invention
One embodiment of the present invention relates to a light-emitting device utilizing electroluminescence. Further, one embodiment of the present invention relates to an electronic device using the light-emitting device.
2. Description of the Related Art
In recent years, research and development have been extensively conducted on light-emitting elements using electroluminescence (EL). In a basic structure of such a light-emitting element, a layer containing a light-emitting substance is interposed between a pair of electrodes. By applying a voltage to the element, light emission can be obtained from the light-emitting substance.
Since the light-emitting element is a self-luminous type, a light-emitting device using this light-emitting element has advantages such as high visibility, no necessity of a backlight, low power consumption, and the like. Further, such a light-emitting element also has advantages in that the element can be formed to be thin and lightweight and that response time is high.
In order to improve flexibility and impact resistance in addition to its thinness and lightness, a flexible substrate has been proposed to be used in a light-emitting device including the light-emitting element. The flexible substrate is applied not only to the light-emitting device but also to a semiconductor device or the like which functions by utilizing semiconductor characteristics.
As a method for manufacturing semiconductor device using a flexible substrate, a technique in which after a semiconductor element such as a thin film transistor is formed over a base material such as a glass substrate or a quartz substrate, the semiconductor element is transferred from the base material to another base material (e.g., a flexible substrate) has been developed. In order to transfer the semiconductor element to another base material, a step for separating the semiconductor element from the base material that is used in manufacturing the semiconductor element is necessary.
In addition, Patent Document 1 discloses a technique in which separation is conducted by physical force such as human hands. In Patent Document 1, a metal layer is formed between a substrate and an oxide layer and separation is generated at the interface between the oxide layer and the metal layer by utilizing weak bonding at the interface between the oxide layer and the metal layer, so that a layer to be separated and the substrate are separated from each other.
In Patent Document 1, an intermediate insulating layer is formed over the light-emitting element including an anode, an organic light-emitting layer, and a cathode, and the intermediate insulating layer is bonded to a supporting member using an adhesive layer (a bonding layer). Then, separation is performed at the interface between the oxide layer and the metal layer, and the layer to be separated which includes the light-emitting element is attached onto a film substrate using the adhesive layer, whereby a light-emitting device including a flexible substrate is manufactured.
A technique in which a highly airtight sealed structure is formed in such a manner that two substrates are bonded to each other by a glass layer containing low-melting frit glass is known. In a technique disclosed in Patent Document 2, a paste containing a binder and a low-melting glass frit material is applied to a glass substrate along the edge of the glass substrate, the binder is removed and the frit material is melted to form frit glass by baking of the paste, and the frit glass is irradiated with laser light with the substrate overlapping with a counter substrate so that the substrate and the counter substrate are bonded to each other with the frit glass provided therebetween; thus, a highly airtight sealed body is formed.
Such frit glass has a high gas barrier property; thus, the sealed space can be kept away from the external atmosphere. A method of sealing using such frit glass is applied to a device including an element (e.g., an organic EL (electroluminescent) element) whose performance is rapidly impaired once the element is exposed to air (including moisture or oxygen).